![Transition temperature of s‐SVP and the corresponding copolymers and composites. a) Melting temperature versus carbon atoms of the side‐chain in various s‐SVP. Reproduced with permission.[⁷⁹] Copyright 2014, Royal Society of Chemistry. b) Differential scanning calorimetry (DSC) of alkylated poly(vinyl chloride) with different side‐chain carbon atom numbers. Reproduced with permission.[⁷⁷] Copyright 2018, Elsevier. c) DSC of stearyl acrylate, tetradecyl acrylate, and its copolymers. Reproduced with permission.[⁵⁰] Copyright 2021, Elsevier Inc. d) DSC of stearyl acrylate—urethane diacrylate copolymers of different ratios. Reproduced with permission.[⁵²] Copyright 2016, American Chemical Society. e) DSC of allyl‐based epoxy resin—paraffin composites of different ratios. Reproduced with permission.[⁹⁹] Copyright 2018, American Chemical Society. f) DSC of composites comprising poly(stearyl methacrylate) and n‐alkanes series with different alkyl chain lengths. Reproduced with permission.[¹⁰⁰] Copyright 2020, The American Association for the Advancement of Science.](https://www.researchgate.net/publication/358375113/figure/fig4/AS:11431281173204426@1688786424727/Transition-temperature-of-s-SVP-and-the-corresponding-copolymers-and-composites-a_Q320.jpg)
![Mechanical property of s‐SVP copolymers and composites. a) Storage modulus of hexadecyl acrylate‐stearyl acrylate copolymers as a function of temperature. Reproduced with permission.[¹⁰¹] Copyright 2020, American Chemical Society. b) Effects of introducing different ratios of urethane diacrylate into stearyl acrylate polymer on storage modulus. Reproduced with permission.[⁵²] Copyright 2016, American Chemical Society. c) The storage modulus measurement of s‐SVP reinforced by bacterial cellulose nanofibers at different states. Reproduced with permission.[¹⁰¹] Copyright 2020, American Chemical Society. d) Tensile stress–strain curve of s‐SVP and s‐SVP ‐acrylic acid composite above the transition temperature. Reproduced with permission.[¹⁰⁴] Copyright 2018, American Chemical Society. e) Storage modulus at varied temperature of s‐SVP incorporated with tridentate Fe(III)—carboxylate reversible group under association/dissociation stimuli. Reproduced with permission.[¹⁰⁵] Copyright 2018, Wiley‐VCH. f) Quintuple‐switching mechanics of composites comprising poly(stearyl methacrylate) and n‐alkanes series with different alkyl chain lengths. Reproduced with permission.[¹⁰⁰] Copyright 2020, published by The American Association for the Advancement of Science.](https://www.researchgate.net/publication/358375113/figure/fig5/AS:11431281173223238@1688786424826/Mechanical-property-of-s-SVP-copolymers-and-composites-a-Storage-modulus-of-hexadecyl_Q320.jpg)
March 2022
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30 Citations
Stiffness variable materials have been applied in a variety of engineering fields that require adaptation, automatic modulation, and morphing because of their unique property to switch between a rigid, load‐bearing state and a soft, compliant state. Stiffness variable polymers comprising phase‐changing side‐chains (s‐SVPs) have densely grafted, highly crystallizable long alkyl side‐chains in a crosslinked network. Such a bottlebrush network‐like structure gives rise to rigidity modulation as a result of the reversible crystallization and melting of the side chains. The corresponding modulus changes can be more than 1000‐fold within a narrow temperature span, from ≈10² MPa to ≈10² kPa or lower. Other important properties of the s‐SVP, such as stretchability, optical transmittance, and adhesion, can also be altered. This work reviews the underlying molecular mechanisms in the s‐SVP's, discusses the material's structure–property relationship, and summarizes important applications explored so far, including reversible shape transformation, bistable electromechanical transduction, optical modulation, and reversible adhesion.